1. Field of the Invention
The present invention relates to a high-speed tool steel which can exhibit, through an ordinary hardening-and-tempering treatment, a high hardness of HRC 71 or higher.
2. Description of the Prior Art
Hitherto, only few proposals have been made as to high-speed tool steels having high hardness of HRC 71 or higher. These proposals are made only partially in Japanese Patent Publication No. 6096/80 entitled "Hard Alloy", Japanese Patent Publication No.21 42/82 entitled "High-Speed Tool Steel Enriched with Carbides", Japanese Patent Application Laid-Open Publication No. 181367/82 entitled "Sintered High-V High-Speed Tool Steel and Method of Producing the Same", and Japanese Patent Application Laid-Open Publication No. 181848/83 entitled "Nitride-Containing Sintered High-V High-Speed Tool Steel and Method of Producing the Same".
According to the known techniques, in order to obtain a high hardness of HRC 71 or higher, it is necessary to increase the content of expensive alloying element such as W, Mo, V, etc., or to disperse a large amount of hard substance such as TiN, etc., resulting in various inconveniences such as a rise in the production cost and deteriorations of machinability and toughness. For instance, in the embodiment shown in Japanese Patent Publication No. 2142/82, only the steel samples Nos. 5 and 11 (Tables 1 and 2) provide the high hardness of HRC 71 or higher. These steels, however, have impractically high contents of W+2Mo of 49.0% and 49.7%, respectively.
Also in the embodiment shown in Japanese Patent Application Laid-Open Publication No. 181367/82, a hardness of HRC 71 or higher is obtained only when the V content is increased beyond 25% (see FIG. 2). Further, also in case of the steel disclosed in Japanese Patent Application Laid-Open Publication No. 181848/83, a high hardness of HRC 71 or higher cannot be obtained unless the TiN is dispersed by an amount not smaller than 15%.